import pygame
from pygame.sprite import Sprite


class Ship(Sprite):

    def __init__(self, ai_settings, screen):
        """初始化船，并设置其起始位置。"""
        super(Ship, self).__init__()
        self.screen = screen
        self.ai_settings = ai_settings

        # 加载飞船图像，并获取其图像.
        self.image = pygame.image.load('images/ship.png ')
        self.rect = self.image.get_rect()
        self.screen_rect = screen.get_rect()

        # 在屏幕的底部中心开始每艘新船.
        self.rect.centerx = self.screen_rect.centerx
        self.rect.bottom = self.screen_rect.bottom

        # Store a decimal value for the ship's center.
        self.center = float(self.rect.centerx)

        # Movement flags.
        self.moving_right = False
        self.moving_left = False

    def center_ship(self):
        """在屏幕上将船居中。"""
        self.center = self.screen_rect.centerx

    def update(self):
        """根据运动标记更新船的位置。"""

        if self.moving_right and self.rect.right < self.screen_rect.right:
            self.center += self.ai_settings.ship_speed_factor
        if self.moving_left and self.rect.left > 0:
            self.center -= self.ai_settings.ship_speed_factor

        self.rect.centerx = self.center

    def blitme(self):
        """在当前位置绘制船."""
        self.screen.blit(self.image, self.rect)
